The invention relates to a process and a routing system for dynamic traffic control in a communication network.
Nonhierarchically organized, line-switching communication networks require dynamic routing which adapts itself to the respective traffic load in the network in a way which optimizes network throughput. This includes in particular that unbalanced load situations have to be eliminated by the routing.
As in the case of conventional routing in hierarchical networks, with dynamic routing it is also first of all attempted to set up connections via one or more of the planned routes, which are usually direct routes. If this is not possible, because for example all the junction trunk groups of the direct route have reached their capacity, the overflow traffic is assigned to alternate routes.
In the selection of alternate routes, there is the fundamental difference between dynamic routing and conventional routing. In the case of conventional routing, administratively specified alternate routes are searched in strict sequence for an idle line or an idle channel ("fixed alternate routing"). As a result, the routing can react only very unsatisfactorily to unplanned, unusual load situations.
In the case of dynamic routing, overflow traffic occurring if assigned to one or more active alternate routes. This active alternate route or these active alternate routes are not fixed, but are selected in a way corresponding to the respective process for dynamic routing or are even newly determined in the case of each call. The advantages of dynamic routing are its robustness and flexibility with respect to unbalanced load situations in the network, which may occur for example due to loads varying at different times (localized high volume of traffic in cases of disasters, for example) and network degradation (failures of line trunk groups, failures of switching units). In addition, uncertainties in network planning can be compensated better.
European Patent EP-B1 0 229 494 discloses a decentralized process for dynamic routing which assigns overflow traffic to an alternate route until said route is no longer available, i.e. until either the primary link of the alternate route is busy, or the origin node receives a clearing message because a transit node is blocked. In this case, the existing alternate route is replaced cyclically or (pseudo)randomly by another alternate route. In another version of the process, the overflow traffic is distributed over a group of a plurality of alternate routes and, if it becomes unavailable, one alternate route is replaced by another alternate route.
This process has the disadvantage that even highly loaded alternate routes keep receiving overflow traffic, even if alternate routes with still low loading are available and the overflow traffic occurring is not offered equally to all the routes with low loading.
European Patent Application 0 372 270 A2 discloses a routing process. According to this process, if it is established that an alternate route is not available, it is briefly excluded from the route fan, i.e. an alternate route is re-included in the route fan after the elapse of a short period of time, which is also varied for each alternate route. The route fan is also reinitialized in the long term (updated), i.e. if the number of alternate routes contained in it drops below a given number.